Solid state lighting arrays are used for a number of lighting applications. For example, solid state lighting panels including arrays of solid state light emitting devices have been used as direct illumination sources, for example, in architectural and/or accent lighting. A solid state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs), which may include inorganic LEDs, which may include semiconductor layers forming p-n junctions and/or organic LEDs (OLEDs), which may include organic light emission layers.
Solid state lighting arrays are used for a number of lighting applications. For example, solid state lighting panels including arrays of solid state light emitting devices have been used as direct illumination sources, for example, in architectural and/or accent lighting. A solid state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs). Inorganic LEDs typically include semiconductor layers forming p-n junctions. Organic LEDs (OLEDs), which include organic light emission layers, are another type of solid state light emitting device. Typically, a solid state light emitting device generates light through the recombination of electronic carriers, i.e. electrons and holes, in a light emitting layer or region.
Solid state lighting panels are commonly used as backlights for small liquid crystal display (LCD) screens, such as LCD display screens used in portable electronic devices. In addition, there has been increased interest in the use of solid state lighting panels as backlights for larger displays, such as LCD television displays.
Although solid state light sources having high coloring rendering index (CRI) and/or high efficiency have been demonstrated, one problem with the large-scale adoption of such light sources in architectural applications is that commercial lighting systems utilize lamps with standardized connectors that are designed to be used with alternating current (ac) power, which may be phase cut using a phase cutting dimmer device. Typically, a solid state lighting source is provided or coupled with a power converter that converts ac power into dc power, and the dc power is used to energize the light source. However, the use of such power converters may increase the cost of the lighting source and/or the overall installation, and may reduce efficiency.
Some attempts at providing solid state lighting sources have involved driving an LED or string or group of LEDs using a rectified ac waveform. However, because the LEDs require a minimum forward voltage to turn on, the LEDs may turn on for only a part of the rectified ac waveform, which may result in visible flickering, may undesirably lower the power factor of the system, and/or may increase resistive loss in the system.
Other attempts at providing ac-driven solid state lighting sources have involved placing LEDs in an anti-parallel configuration, so that half of the LEDs are driven on each half-cycle of an ac waveform. However, this approach requires twice as many LEDs to produce the same luminous flux as using a rectified ac signal.